1. Field of the Invention
The present invention relates to an electrolytic solution including an electrolyte salt and a battery using the electrolytic solution.
2. Description of the Related Art
In recent years, a large number of portable electronic devices such as camcorders, digital still cameras, cellular phones, personal digital assistants and laptop computers have been emerged, and an attempt to reduce the size and the weight of them has been made. Research and development aimed at improving the energy densities of batteries used as portable power sources of the electronic devices, specifically secondary batteries have been actively promoted. Among the batteries, a lithium-ion secondary battery using a carbon material for an anode, a composite material of lithium (Li) and a transition metal for a cathode and a carbonate for an electrolytic solution can obtain a high energy density, compared to a lead-acid battery and a nickel cadmium battery in related arts, so the lithium-ion secondary battery has been widely put into practical use.
Moreover, recently a further improvement in capacity has been desired according to enhancement of performance of portable electronic devices, and the use of tin (Sn) or silicon (Si) as an anode active material instead of the carbon material has been studied. It is because the theoretical capacities of tin and silicon are 994 mAh/g and 4199 mAh/g, respectively, which are much larger than the theoretical capacity of graphite of 372 mAh/g, therefore, an improvement in capacity can be expected. In particular, it is reported that in an anode formed through forming a thin film of tin or silicon on a current collector, the anode active material is not pulverized by insertion and extraction of lithium, and a relatively large discharge capacity can be maintained (for example, refer to the pamphlet of International Publication No. WO01/031724).
Further, as a secondary battery capable of obtaining a high energy density, there is a lithium metal secondary battery using lithium metal for an anode and using only precipitation and dissolution reactions of lithium metal for an anode reaction. The lithium metal has a theoretical electrochemical equivalent of 2054 mAh/cm3, which is 2.5 times larger than that of graphite, so the lithium metal secondary battery holds promise of improving the capacity. A large number of researchers have been conducting research and development aimed at putting the lithium metal secondary battery to practical use (for example, refer to “Lithium Batteries” Edited by Jean-Paul Gabano, Academic Press, 1983, London, New York).
Further, a secondary battery in which the capacity of an anode includes a capacity component by insertion and extraction of lithium and a capacity component by precipitation and dissolution of lithium, and is represented by the sum of them has been developed recently (for example, refer to the pamphlet of International Publication No. WO01/22519). In the secondary battery, a carbon material capable of inserting and extracting lithium is used for an anode, and lithium is precipitated on a surface of the carbon material during charge. The secondary battery holds promise of achieving a high energy density as in the case of the lithium metal secondary battery.